Audio video bridging (AVB) technology has gained renewed interest in recent times. AVB started with a focus on protocols that allow time-synchronized low latency services through IEEE 802 networks, such as Ethernet, for audio and video transmissions.
More recently, efforts have been made to utilize AVB technology and related protocols, such as the Stream Reservation Protocol (SRP), for any type of time-sensitive stream. These efforts have been defined under the IEEE 801.1Q-2014 standard as Forwarding and Queuing of Time-Sensitive Streams (FQTSS). In one conventional implementation of FQTSS, multiple streams may be multiplexed to facilitate transmission across a physical layer (PHY) from an endpoint as a packet stream.
Conventional implementations of the FQTSS standard are considered wasteful with respect to bandwidth for a variety of reasons. The FQTSS standard describes, and conventional implementations utilize, bandwidth measurement intervals that occur at 125 us and 250 us. Each stream may include one or more packets that are aligned with a queue for transmission. Packets from each queue may be scheduled for transmission at each bandwidth measurement interval—e.g., every 125 us. If a particular queue is determined to have priority over other queues at this interval, the endpoint may schedule transmission of any packets in that queue. The number and size of the scheduled packets from this queue may vary and can amount to less than 125 us worth of information to transmit. As a result, in a conventional endpoint, if there is less than 125 us worth of packets scheduled for transmission, the endpoint transmits the scheduled packets and remains idle until the next bandwidth measurement interval occurs (125 us after scheduling packets for transmission). At the next bandwidth measurement interval, the next set of packets are scheduled for transmission. However, idle time during which no packets are sent is considered wasteful with respect to available bandwidth.
It should also be noted that the conventional scheduling described above can significantly limit deterministic operation for lower priority queues or classes of information. Consider, for example, the endpoint described above and where approximately 10 us worth of high priority packets queue every 110 us. The endpoint may not only waste bandwidth transmitting these high priority packets as described above, but also this reduced bandwidth limits the available bandwidth for the lower priority packets. As a result, the endpoint may become incapable of satisfying deterministic operation for more than a couple priority classes of packets. For instance, if there were four priority classes or queues, one of which is high priority in the example case provided, the available bandwidth to the remaining three priority classes may be significantly less than the full bandwidth of the communication link, and possibly less than the amount of bandwidth necessary to satisfy deterministic behavior for the remaining three priority classes.